switching from a non tach to a tach,what wires do I have to hook up,thanks 81 f100 stepside inline 6 auto

 

When I installed the tach in my 84, I did not have to connect any wires. I just plugged it into the same harness. My truck originally came with the 300 and now I have a 460 in it. But I never had the tach dash in the truck with the 300. With the 460 it works fine.

I hope this helps

Mudman

 

If your original instrument cluster had an ammeter and oil pressure gauge then the cluster with tach should be pretty much plug-in and go except the brake warning and turn indicator light positions might be reversed. If so, swap positions of the little colored plastic inserts in the instrument panel cover assembly. If the original cluster had oil pressure and charging "idiot lights" then there are several wiring changes in addition to changing the voltage regulator (and possibly the alternator) and oil pressure sending unit to make the tachometer, ammeter and oil pressure gauge work. You would likely be better off just adding the tachometer and necessary tach wiring to the existing "idiot light" cluster. From the wiring diadram in my Haynes manual it appears the tachometer only requires 2 wires: Ground, and Tach signal (from tach terminal on ignition coil). Unfortunately, I cannot describe to which actual terminals on the tachometer these wires attach. If you hook it up and it doesn't work, reverse the wires.

 

tach does not work by just pluging in harness,must be a wire I have to connect

 

Looks like the 300 six wiring harness doesn't have a ground wire for the tach. On the instrument panel printed wiring circuit trace back to the connector to find out which tach wires are missing in the harness.

 

Maybe the tach is broken.

 

Do a search in this forum for tach and you should find your info..... from memory ( oh no!) I agree if you have gauges and not idiot lights start by just plugging it in. There is 1 wire that either needs connected or not and it depends whether you are putting it in a 6 cylinder or an 8.

Hope this helps!

 

Has anyone ever put a stock (optional) tach on a six cyl? If so, does it read correctly? Looks like to me it would read incorrectly at 3/4 the actual rpm since (as best I can tell) there is no way to compensate for the fewer number of ignition pulses per revolution on the six versus the eight. Aftermarket tachs usually have a switch to let you choose among 4, 6 or 8 cylinders to match your engine. I don't remember seeing any adjustments or switches on the tach or instrument panel when I converted my '83 to the tach equipped instrument panel several years ago.

 

It seems I remember from old threads that it's purely "plug and play"...and somehow the tach knows it's a six.

 

Its just plug and play. I had a tach cluster in my old 82 with a 300 six. It worked perfectly and read correctly also.

I still wonder how the tach knew it was a 6 though?

 

pluged and no play,guess maybe an 81 is diferent.all other gauges work fine,just have to switch turn indicaters

 

I put a tach cluster on my '83 with a 300. It came out of an '86 with the 302. It was just a plug and play on mine. I even left the after market tach in it for a couple days to make sure it worked right. Both tachs read exactly the same. My truck did originally have full gages, just no tach.

 

I thought I read there was 1 wire different between a 6 and an 8.... but if it's plug and play then great...... I can't imagine it looks at the cylinders tho- more apt to look at how many times something has "gone around" like the distributor etc.) A circle is always 360 degrees and it's still a circle if there are 6 or 8 pieces to it!

( c'mon somebody knowledgeable - tell us how it works!!!)

 

I just looked it up in my Ford 1983 Truck Shop Manual which I quote; "The tachometer ... can be used on either 6 cylinder or 8 cylinder engines. The tachometer terminals "B" (+12 volts), "C" (coil negative), and "G" (ground) are used for 6 cylinder engines. A fourth terminal "8" (8 cyl. ground) is grounded through the wire harness for 8 cylinder engine operation."
Deluxe cluster tach wiring:
Tach terminal C = Instrument Cluster Connector Pin 11 (- side ign. coil terminal)
" " B = " " " " 13 (+ 12 v. in "run")
" " G = " " " " 2 (ground, all)
" " 8 = " " " " 12 (ground, 8 Cyl only)

I believe the "deluxe cluster" is "plug and play" only for vehicles originally equipped with gauges and not for "idiot light" cluster equipped vehicles. You should be able to wire the tach to operate in an "Idiot Light" cluster by supplying external wiring directly to the tach terminals as listed above. I suspect the 8 terminal, when grounded, adds an additional capacitor in the pulse detection circuit to increase the number of pulses required to charge the detector circuit to the same voltage level as that of the 6 cylinder at the same RPM.

 

Excellent research.
Mr Moderator....this should be made a "sticky".